In a case where an electronic document displayed on a personal computer (hereinafter, referred to as “PC”) is to be sealed (that is, to form a seal image), it was necessary to print out the electronic document, stamp a seal impression onto a document thus printed out, and then, scan in by a scanner the document having the seal impression thus stamped, so as to convert the document into an electronic document again. However, development of software capable of carrying out a process of adding a user's seal image onto an electronic document displayed on a PC (i.e., electronic seal software) made it possible to directly add, by operating a keyboard and mouse of a PC, a pre-registered seal image onto a displayed electronic document, without printing out the electronic document in order to stamp the seal impression thereon.
[Patent Document 1]
    Japanese Unexamined Patent Publication No. 2006-209713 (Tokukai 2006-209713, publication date: Aug. 10, 2006)[Patent Document 2]    Japanese Unexamined Patent Publication No. 2006-179977 (Tokukai 2006-179977, publication date: Jul. 6, 2006)
In a system utilizing electronic seal software, it is understandably necessary to prevent a fraud in which an unauthorized person operates the system in order to add a seal image of a person other than the unauthorized person onto an electronic document without permission. Therefore, user authentication should be performed before a process of sealing. The user authentication is reliably performed by finger authentication in which a feature of a user's digit (a fingerprint, a vein pattern, etc.) is verified.
In order to perform finger authentication in a system utilizing electronic seal software, it is necessary to externally attach to a PC a finger authentication scanner solely dedicated for reading an image from a digit, or, it is necessary to use a notebook PC having a built-in finger authentication scanner solely dedicated for reading an image from a digit. In view of this, there is a demand for a system in which electronic sealing can be performed after finger authentication is performed without a finger authentication scanner or a notebook PC having a built-in finger authentication scanner.